The present invention pertains to a vehicle heating system in general and more particularly to a vehicle heating system with (a) a heater that is able to generate heat by burning fuel and release it to a liquid heat carrier, (b) a heat carrier circuit including a feed line leading from the driving internal combustion engine of the vehicle to the heater and from the heater to a heating heat exchanger for the vehicle interior, and a return line leading from the heating heat exchanger to the internal combustion engine, and (c) a control device for the heater, which controls the operation of the heater, based on the heat carrier temperature determined behind the heater in the heat carrier circuit.
In conventional vehicle heaters of this class, the heat carrier heated in the heater flows through the heating heat exchanger and from there--normally with a still very high heat content--through the internal combustion engine before it again reaches the inlet side of the heater. Even though this ensures, for example, good preheating of the internal combustion engine before a cold start in winter, the heat carrier is returned to the heater in an intensely cooled state because of the considerable heat losses in lines of considerable length and due to the release of considerable amounts of heat in the internal combustion engine. Unless a very large dimensioned heater is installed, a rather long time is required for reliable deicing of the vehicle and the heating of the vehicle interior to a comfortable temperature. Valuable current is consumed from the vehicle battery during this time, aside from the fuel consumption of the heater during this period. The battery is normally very low in absolute terms. Furthermore, a large percentage of the possible heat transfer capacity of the heating heat exchanger is not utilized, especially at low outside temperatures, at which the heater is unable to heat the intensely cooled heat carrier to a desirable, high outlet temperature.